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JavaScript Operators
Addition Assignment Operator (+=) (JavaScript)
Addition Operator (+) (JavaScript)
Assignment Operator (=) (JavaScript)
Bitwise AND Assignment Operator (&=) (JavaScript)
Bitwise AND Operator (&) (JavaScript)
Bitwise Left Shift Operator (<<) (JavaScript)
Bitwise NOT Operator (~) (JavaScript)
Bitwise OR Assignment Operator (|=) (JavaScript)
Bitwise OR Operator (|) (JavaScript)
Bitwise Right Shift Operator (>>) (JavaScript)
Bitwise XOR Assignment Operator (^=) (JavaScript)
Bitwise XOR Operator (^) (JavaScript)
Comma Operator (,) (JavaScript)
Comparison Operators (JavaScript)
Compound Assignment Operators (JavaScript)
Conditional (Ternary) Operator (?:) (JavaScript)
delete Operator (JavaScript)
Division Assignment Operator (/=) (JavaScript)
Division Operator (/) (JavaScript)
in Operator (JavaScript)
Increment (++) and Decrement (--) Operators (JavaScript)
instanceof Operator (JavaScript)
Left Shift Assignment Operator (<<=) (JavaScript)
Logical AND Operator (&&) (JavaScript)
Logical NOT Operator (!) (JavaScript)
Logical OR Operator (||) (JavaScript)
Modulus Assignment Operator (JavaScript)
Modulus Operator (JavaScript)
Multiplication Assignment Operator (*=) (JavaScript)
Multiplication Operator (*) (JavaScript)
new Operator (JavaScript)
Right Shift Assignment Operator (>>=) (JavaScript)
Subtraction Assignment Operator (-=) (JavaScript)
Subtraction Operator (-) (JavaScript)
typeof Operator (JavaScript)
Unsigned Right Shift Assignment Operator (>>>=) (JavaScript)
Unsigned Right Shift Operator (>>>) (JavaScript)
void Operator (JavaScript)
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Addition Assignment Operator (+=) (JavaScript)

JavaScript - Internet Explorer 10

Adds the value of an expression to the value of a variable and assigns the result to the variable.

Copy 
result += expression
result

Any variable.

expression

Any expression.

Using this operator is exactly the same as specifying: result = result + expression.

The types of the two expressions determine the behavior of the += operator.

If

Then

Both expressions are numeric or Boolean

Add

Both expressions are strings

Concatenate

One expression is numeric and the other is a string

Concatenate

Supported in the following document modes: Quirks, Internet Explorer 6 standards, Internet Explorer 7 standards, Internet Explorer 8 standards, Internet Explorer 9 standards, Internet Explorer 10 standards. Also supported in Windows Store apps. See Version Information.

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